1. Field of the Invention
The present invention relates to a coding apparatus for processing digital signals; a recording medium for recording signals coded by the coding apparatus; and a reproducing apparatus for reproducing the signals recorded on the recording medium, and more specifically to a signal coding apparatus for coding video signals hierarchically into a plurality of sorts of video signals, multiplexing the coded video signals, and recording the multiplexed video signals on a disklike recording medium of a constant recording density; the disklike recording medium for recording the coded and multiplexed video signals; and the reproducing apparatus for reproducing the multiplexed and recorded video signals from the recording medium.
2. Description of the Prior Art
When video signals are coded at high efficiency, there exists such a case that the video signals are classified into a plurality of sorts of video signals hierarchically, and only the video signals to be reproduced preferentially according to the object are decoded and then reproduced (referred to as priority signals, hereinafter). In this case, even if the non-priority signals other than the priority signals are once read, the read non-priority signals remain unused.
Here, the priority signals reproduced based on priority are signal components of lower frequencies or quantized coarsely from the time and spacial points of view in the hierarchical coding, which can be used alone. On the other hand, the non-priority signals are differential signals between the signals to be coded and the signal components of high frequencies or quantized coarsely from the time and spacial points of view in the hierarchical coding, which cannot be used alone.
For example, in the hierarchical coding of the current TV signals and the HDTV (high definition) signals, there exist video signals having codes of the current TV signals and codes of differential signals between the current TV signals and the HDTV signals. In this case, the HDTV video signals can be obtained by decoding both of the signals (the current TV and the differential HDTV signals) and by adding both of the decoded video signals. On the other hand, when only the current TV signals are required, only the current TV video signals are decoded.
Further, in the case of such a storage media, it is possible to realize a high speed search by seeing the picture. In this case where the interframe prediction is adopted, the video signals in only one frame are coded independently for each several frames. Further, in the case of the high speed search mode, only the video signals coded independently, that is, only the independent video signals are reproduced.
An example of a prior art coding apparatus will be explained with reference to FIG. 1. In FIG. 1, the coding apparatus codes video signals hierarchically at different resolutions according to the current TV signals and the HDTV signals, for instance.
In more detail, in FIG. 1, the video signals inputted through the video input terminal 1 are the HDTV signals, and the inputted HDTV signals are given to a low-pass filter (LPF) 2 and a subtracted (subtrahend) input of a subtracter 3. The frequency band of the inputted signals is limited by the LPF 2 down to about 1/2 in both the vertical and horizontal directions in accordance with the subsampling, and then applied to a subsampler 14. The number of pixels of the applied video signals is further reduced by the subsampler 14 down to about 1/2 in both the vertical and horizontal directions, and then the reduced video signals are given to a coder 11 and an interpolator 4 as the current TV signals.
The current TV signals are DCT (discrete cosine transform) processed by the coder 11, and the transformed coefficients are quantized in an appropriate step width. The coded and compressed video codes are then given to a multiplexer 41.
On the other hand, the pixels omitted by the subsampler 14 are interpolated by the interpolator 4 to obtain the video signals whose number of pixels is the same as that of the input video signals, and then given to a subtracting (minuend) input of the subtracter 3. The interpolated signals are subtracted from the input signals by the subtracter 3 to obtain differential HDTV signals. The obtained differential HDTV signals are given to a coder 5.
The operation of the coder 5 is basically the same as that of the coder 11 for coding the current TV signals, and only the number of sampled signals to be process is different. The video codes outputted by the coder 5 are given to the multiplexer 41.
The codes of the differential HDTV signals and the codes of the current TV signals are multiplexed by the multiplexer 41 for each predetermined quantity of codes, and then outputted through a code output terminal 9. The codes obtained by the coding apparatus as described above are reformed into a code form suitable for the recording medium by a channel encoder, and then recorded on a disklike recording medium (referred to as a disk, hereinafter).
Next, an example of the prior art reproducing apparatus for reproducing the video signals coded by the coding apparatus as shown in FIG. 1 and then recorded on the disk will be described hereinbelow with reference to FIG. 2.
In FIG. 2, the signals recorded in a disklike recording medium (not shown) are read by a signal reader 21 and the read signals are given to a channel decoder 22. The signal reader 21 is composed of a recording medium driving system, a pickup, etc., and the reading positions (track numbers) of the recording medium are controlled by a read controller 27.
The codes are reproduced from the read signals by the channel decoder 22, and then given to a demultiplexer 51 after some processing such as error correction. Further, the track position signals detected by the channel decoder 22 are given to the read controller 27 for control of the reader 21.
The codes of the current TV signals and the codes of the differential HDTV signals multiplexed for each predetermined code quantities are separated from each other by the demultiplexer 51. The current TV signal codes are given to a decoder 29, and the differential HDTV signal codes are given to a decoder 24, respectively.
The codes given to the decoder 24 are replaced with representative values by the reverse quantization processing (reverse DCT processing) by the decoder 24 to obtain the reproduced video signals of the differential HDTV signals. In the same way, the reproduced video signals of the current TV signals can be obtained by the decoder 29.
The output of the decoder 24 is given to an adder 25. The output of the decoder 29 is given to an interpolator 4 to interpolate the reproduced current TV signals to obtain the video signals having the original number of pixels. The obtained reproduced signals are given to an adder 25. The interpolated current TV signals and the differential HDTV signals are added by the adder 25 to obtain the reproduced HDTV signals. The obtained signals are outputted through a video output terminal 26.
In the prior art image coding apparatus, the prior art disklike recording medium, and the prior art reproducing apparatus for the hierarchical video signals as described above, however, since only some specified signals (e.g., low resolution video signals in the hierarchical coding) cannot be reproduced, even when only the specific signals are required to be reproduced, it has been necessary to read unnecessary signals at the same time. In particular, in the case of the disk rotated at a constant linear velocity (referred to as CLV, hereinafter), since the quantity of codes for each one revolution of the disk changes according to the recording positions (the radius of the signal track), the points at which the sorts of recorded signals are switched are not related to the revolution angles of the disk, so that it has been difficult to read only the specific signals.